A common problem associated with using flash photography is the occurrence of a phenomenon known as “red-eye.” When a flash photography device such as a digital camera is used to capture an image, the flash can reflect off of the retina of an eye if the flash source and eye are within approximately five degrees of horizontal alignment. This reflection will cause the eyes of a human subject to appear red in the image. More specifically, the pupil region of the eyes will be red in the image. In a related context, “pet-eye” can occur when the flash reflects off of the retina of an animal eye. In this context, the pupil region of the animal subject's eye will often appear green, but can be various different colors. In either situation, the red, green, or other eye color resulting from the flash is an undesired eye color present in the captured digital image. The desired coloring of the pupil is usually black, which is the naturally appearing color of most pupils.
An advantage of digital imaging is the ability to alter or edit digital images to correct for flaws or undesired effects, such as “red-eye.” Various methods have been devised in the art for correcting red-eye in digital images. However, these methods suffer from several drawbacks. Among these drawbacks is creation of unnatural-looking, gray pupils. For example, a simple desaturation technique will often result in hazy, gray pupils. Some methods achieve blackened pupils, but also result in the removal of the specular reflection from the pupil. The specular reflection is the desired, natural-looking reflection of light off of the pupil. Removal of this reflection results in unnatural-looking pupils that appear to have been artificially altered. One goal of digital image editing is to make an image appear natural without also making it obvious that the image was edited, altered, or enhanced in any way. So, some correction methods suffer from the drawback of generating corrected images that obviously appear to have been altered.
Other correction methods are burdensome on computer system resources. Some correction methods are slow and not well-suited to being applied to numerous images. Other methods are inconsistent and unreliable. For particular digital images, the correction method may perform a fix of acceptable quality, but for other images, bizarre results can occur. For example, some methods can occasionally result in the appearance of halo-like effects on the subject's pupils.